Natural occuring oil seepages as a consequence of bottom trawling?

Abstract

Bottom trawling is used to capture fish species that live in the seabed. The damage on the seabed trawling causes has been discussed for many years. This thesis aims to investigate whether bottom trawling for sand eels can be a cause for some of the detected oil seepages in the North Sea. We investigated this using manual delineation of oil seepages in Synthetic Aperture Radar (SAR) satellite images to create statistics of when and where oil observations have been made; in total three areas were investigated. The SAR observations have been coupled together with wind speed data and trawling tracks. In 2020, an average of 76 % of the oil seepage observations were made during the sand eel trawling season. In 2021 there was a sudden drop in trawling activity with half the total number of trawling tracks. The sudden drop in trawling activ- ity for 2021 greatly reduced the number of observations of oil slicks, but one of the three investigated areas showed a similar number of observations in- side the trawling season. Using the trawling track information it was observed that areas with higher amounts of trawling activity have a higher number of seepage observations. For three of the datasets a p-value below 0.05 was con- firmed, based on a null hypothesis of neither favouring observation of an oil slick during or outside of sand eel trawling season. Notably the statistics of observations implies a significant correlation between trawling activity and oil slick observations, which warrants further study or observation.